1. Field of the Invention
The present invention relates to a spectral characteristic measurement method and a spectral characteristic measurement apparatus for measuring spectral characteristics of measured light with higher accuracy.
2. Description of the Background Art
Conventionally, spectrometry has widely been used as a technique for evaluating an illuminant and the like. In a spectral characteristic measurement apparatus used in such spectrometry, a spectrometer (typically, a diffraction grating) is generally used to split measured light from an illuminant or the like, which is a measurement target, into a plurality of components and to detect each resultant component with a photodetector. In order to minimize influence of light other than light to be measured, the spectrometer and the photodetector are accommodated in a housing.
Actually, however, a result of detection by the photodetector may be affected by irregularly reflected light in the housing, light reflected in a diffused manner at a surface of the spectrometer, light having an order other than a measurement order, and the like. In general, such light is referred to as “stray light”. Various methods have been proposed in order to suppress influence of such unintended stray light.
For example, Japanese Patent Laying-Open No. 11-030552 discloses a method of correcting stray light by accurately estimating influence of the stray light generated in measurement of light guided from a dispersion optical system of a spectrophotometer with a light receiver having a large number of light-receiving elements as a measurement constant of the spectrophotometer and by eliminating that influence.
In addition, Japanese Patent Laying-Open No. 2002-005741 discloses a spectrum measurement apparatus capable of obtaining an accurate spectrum intensity signal by eliminating influence of stray light generated within the spectrum measurement apparatus or unnecessary light generated by reflection or diffraction at a surface of a detection element through processing of a detection signal.
Further, Japanese Patent Laying-Open No. 2010-117343 discloses an optical characteristic measurement apparatus for measuring a spectrum in a shorter period of time with higher accuracy by calculating a correction value based on signal intensity detected in a correction area (an area where light split by a spectrometer is not incident) and calculating a corrected measurement spectrum by subtracting the calculated correction value from each component value included in a measurement spectrum detected in a detection area (an area corresponding to a surface on which light from the spectrometer is incident).
Furthermore, Japanese Patent Laying-Open No. 2009-222690 discloses an inexpensive optical measurement instrument capable of removing stray light from measurement data.